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Register a new userConstraining gluon density of pions at large $x$ by pion-induced $J/psi$ production
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The gluon distributions of the pion obtained from various global fits exhibit large variations among them. Within the framework of the color evaporation model, we show that the existing pion-induced $J/psi$ production data, usually not included in the global fits, can impose useful additional constraints on the pion parton distribution functions (PDFs). In particular, these data can probe the pions gluon densities at large $x$. Existing pion-induced $J/psi$ data covering a broad range of beam momenta are compared with next-to-leading-order QCD calculations using various sets of pion PDFs. It is found that $J/psi$ data measured at forward rapidity and at sufficiently high beam momentum are sensitive to the large-$x$ gluon distribution of pions. The current $J/psi$ data favor the Sutton-Martin-Roberts-Stirling and Gluck-Reya-Vogt pion PDFs, containing significant gluon content at large $x$.
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We propose to use transverse momentum $p_T$ distribution of $J/psi$ production at the future Electron Ion Collider (EIC) to explore the production mechanism of heavy quarkonia in high energy collisions. We apply QCD and QED collinear factorization to the production of a $cbar{c}$ pair at high $p_T$, and non-relativistic QCD factorization to the hadronization of the pair to a $J/psi$. We evaluate $J/psi$ $p_T$-distribution at both leading and next-to-leading order in strong coupling, and show that production rates for various color-spin channels of a $cbar{c}$ pair in electron-hadron collisions are very different from that in hadron-hadron collisions, which provides a strong discriminative power to determine various transition rates for the pair to become a $J/psi$. We predict that the $J/psi$ produced in electron-hadron collisions is likely unpolarized, and the production is an ideal probe for gluon distribution of colliding hadron (or nucleus). We find that the $J/psi$ production is dominated by the color-octet channel, providing an excellent probe to explore the gluon medium in large nuclei at the EIC.
The production mechanism of quarkonia states in hadronic collisions is still to be understood by the scientific community. In high-multiplicity $p+p$ collisions, Underlying Event (UE) observables are of major interest. The Multi-Parton Interactions (MPI) is a UE observable, where several interactions occur at the partonic level in a single $p+p$ event. This leads to dependence of particle production on event multiplicity. If the MPI occurs in a harder scale, there will be a correlation between the yield of quarkonia and total charged particle multiplicity. The ALICE experiment at the Large Hadron Collider (LHC) in $p+p$ collisions at $sqrt{s}$ = 7 and 13 TeV has observed an approximate linear increase of relative $J/psi$ yield ($frac{dN_{J/psi}/dy}{<dN_{J/psi}/dy>}$) with relative charged particle multiplicity density ($frac{dN_{ch}/dy}{<dN_{ch}/dy>}$). In our present work we have performed a comprehensive study of the production of charmonia as a function of charged particle multiplicity in $p+p$ collisions at LHC energies using pQCD-inspired multiparton interaction model, PYTHIA8 tune 4C, with and without Color Reconnection (CR) scheme. A detail multiplicity and energy dependent study is performed to understand the effects of MPI on $J/psi$ production. The ratio of $psi(2S)$ to $J/psi$ is also studied as a function of charged particle multiplicity at LHC energies.
We study the inclusive J/psi production at large transverse momenta at lepton-hadron colliders in the limit when the exchange photon is quasi real, also referred to as photoproduction. Our computation includes the leading-P_T leading-v next-to-leading alpha_s corrections. In particular, we consider the contribution from J/psi plus another charm quark, by employing for the first time in quarkonium photoproduction the variable-flavour-number scheme. We also include a QED-induced contribution via an off-shell photon which remained ignored in the literature and which we show to be the leading contribution at high P_T within the reach of the EIC. In turn, we use our computation of J/psi+charm to demonstrate its observability at the future EIC and the EIC sensitivity to probe the non-perturbative charm content of the proton at high x.
We argue that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements. A scenario accounting for intermediate $cbar(c)$ interactions is proposed that reproduces the data at low- and mid-range transverse momenta P_T from the Fermilab Tevatron and BNL Relativistiv Heavy Ion Collider. The J/psi produced in this manner are polarized predominantly longitudinally.
We study sub-threshold heavy quarkonium ($J/psi$ and $Upsilon$) photo-productions in $gamma A$ collisions as an independent test of the universality of the nucleon-nucleon short range correlation (SRC) in nuclear scattering processes. Just below the $gamma p$ threshold, the cross section is dominated by the mean field contribution of nucleons inside the nucleus. The SRC contributions start to dominate at lower photon energies, depending on the fraction of the SRC pairs in the target nucleus. We give an estimate of the cross sections in the sub-threshold region both for $J/psi$ and $Upsilon$. This may be helpful for future measurements at JLab as well as at the Electron-Ion Collider in the U.S., and especially in China.
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